SANGIN, Afghanistan – Sgt. Johnathan Cook’s instructions to his Marines were clear before they pushed Tuesday morning into the notorious “Fish Tank” section of Sangin.

“Everyone knows the atmospherics yesterday got a little weird,” he said. “Keep your head on a swivel. We all know the summer offensive is supposed to start in the next 10 days, so expect we could take contact any time.”

The ominous directive came before photographer James Lee and I left Patrol Base Fulod with his unit, an element of Baker Company, 1st Battalion, 7th Marines, out of Twentynine Palms, Calif. Second Squad, 3rd Platoon, had patrolled nearby the day before, and observed wearily that villagers were avoiding them.

After more than a week of relative peace in Sangin, was the honeymoon over?

The squad patrolled this morning through what is historically one of the most dangerous sections of Sangin district, where dozens of Marines have been killed since summer 2010.

Sangin is famous for the lush fields of poppy and wheat in its Green Zone, but there also is a Brown Zone to the southeast of Route 611, farther away from the Helmand River. The Fish Tank is one of its signature areas. It was named by British forces, who gave several bases in the region “fishy” names like “Shark,” before the U.S. took over security in August 2010.

Unlike the Green Zone, the Fish Tank has few open spaces. It’s a maze of tight alleys, tiny doorways, sharp angles and 10-foot mud walls. Marines there have little chance to determine what faces them around the next bend – until danger is potentially upon them.

Advice I received this morning underscores that. Before the patrol, Cpl. Manuel Espinoza, a fire team leader, cheerfully suggested that if a firefight broke out, I should not only avoid diving for cover onto turf not scanned for improvised explosive devices (which I knew), but also brush the ground in front of me before dropping to one knee.

“You don’t want to go down on a toe-popper,” he said. “It’ll blow your kneecap off.”

The patrol itself moved more deliberately than any of the estimated 20 I’ve been on in my career with Marine Corps Times. Whenever possible, the Marines stayed on hard-packed trails, where it’s more difficult to emplace IEDs. They also backtracked out of at least three alleys after deciding that there wasn’t enough tactical value to go through them. Staying on roads that villagers travel frequently is the best way to avoid taking steps that can alter or end a life, they reason.

(James J. Lee/Staff) Lance Cpl. Jedidiah Morgan jumps a low wall rather than walk around it, bypassing a potential IED choke point during a patrol.

The squad’s personnel also communicated much more frequently than most of the small units I’ve seen in action. They pointed out seemingly sinister piles of stones that could be booby-trapped and investigated a number of “murder holes” — spots in which enemy fighters can open fire at coalition forces behind the relative safety of a wall.

“There are a lot of murder holes here,” Cook said midway through the patrol, pointing out a potential ambush spot. “Half the time when you take fire, you don’t even know where it’s coming from.”

Third Platoon’s squads began patrolling the Fish Tank early in April after deploying, and were tested early, the Marines said. Within days, the Marines were attacked several times with both small-arms fire and grenades, but no Marines have been seriously injured in the area since 1/7 deployed. An interpreter was medically evacuated after sustaining gunshot wounds to both legs, however.